1. Field of the Invention
This invention relates to an image display medium having a memory characteristic and its image writing apparatus, and more particularly to an image display medium with high reliability and capable of realizing cost reduction, compactness and flexibility, and an image writing apparatus capable of realizing compactness.
2. Description of the Related Art
In recent years, as an image display medium, in addition to a paper medium and an electronic display device, the image display medium called electronic paper or digital paper having both advantages of the electronic display device and paper has been widely noticed.
This image display medium, which has the memory characteristic for display, has only to be supplied with energy for write by a driving device or an external information writing device only when information is rewritten, and is not required to be supplied with energy for maintaining the display. So it is possible to take out only the image display medium from the image writing apparatus after the information has been written so that it is carried easily like a sheet medium, superposed or arranged to write the information on a hand.
As the image display medium having the memory characteristic as described above, known are an optical-writing type image display medium in which the image is visually and erasably stored and an image writing apparatus for writing the image into the image display medium (For example, JP-A-2001-301233 ([0044]-[0047], FIG. 4).
The image display medium described in JP-A-2001-301233 has a liquid crystal layer and a photoconductive layer whose resistance is varied by light irradiation which are stacked between a pair of transparent electrodes. In the apparatus for writing the image on the image display medium, with the image display medium transported from a storage unit being in intimate contact with a liquid optical crystal output device, the image is displayed on the liquid crystal optical output device illuminated with backlight from background and the image light is projected onto the photoconductive layer of the image display medium so that a resistance distribution based on an optical pattern is generated on the photoconductive layer. And a divided voltage distribution based on the resistance distribution in the photoconductive layer is applied to the liquid crystal layer by applying a voltage between the transparent electrodes so that the image corresponding to the divided voltage distribution is recorded on the liquid crystal layer.
Generally, the manufacturer of the image display medium is different from the manufacturer for its driving circuit and others. Therefore the LSI and others constituting the driving circuit are not mounted on a mounting board of the image display medium. A power source and an electric signal for display driving is supplied through a flexible board, and for its connecting processing, terminals and soldering are employed.
However the connection using the flexible board is likely to generate short-circuiting, electrical corrosion and wire break among the terminals and electrodes, and is low in the reliability to vibration. In order to obviate such an inconvenience, by converting the electrical signal into an optical signal through e.g. LED and also receive the optical signal from the LED by a light receiving element located at a usual electrode position so that an electric signal is obtained through photoelectric conversion, a photo-coupler device making unnecessary the connection by the flexible board has been proposed (for example, JP-A-8-201782 ([0016], [0017], FIG. 1, FIG. 2).